Field of the Invention
This invention relates to devices for maintaining a heat pump system in normal operating condition and particularly relates to filter-driers for purifying the liquid refrigerant.
Heat pump and refrigeration systems, in which flow in the high-pressure liquid line of the system is reversed when the system is changed from heating to cooling, cooling to defrost or vice versa, are becoming of growing importance. To obtain proper filtration and contaminant retention, two filter-driers are normally combined with external check valves so that flow through each filter-drier is always in the same direction. The reason for such unidirectional flow is to enable a filter-drier to properly perform its filtration function at all times, because if the flow in the unidirectional device is reversed, some of the solid contaminant retained in the filter media can and will be flushed back into the system.
Devices which utilize a plurality of check valves include U.S. Pat. No. 3,299,661 for a check-valve manifold, containing three spherical balls which combine the function of four check valves in a bi-directional heat pump system that enables flow into the expansion valve to be unidirectional, regardless of the position of the reversal valve.
U.S. Pat. No. 3,311,454 describes a testing apparatus which includes a holding chamber between a pair of top and bottom portions and a centrally disposed tube of transparent material with a pair of ball check valves at the ends thereof.
U.S. Pat. No. 3,731,678 describes a respirator for removing smoke and noxious fumes from air before inhaling thereof. It comprises a casing filled with absorbent material and a coaxially disposed conduit which is closed at its lower end by a flapper-type exhalation check valve. A flapper-type inhalation check valve also covers the air outlet openings from the casing.
As an example of the state of the art of heat pump systems, U.S. Pat. No. 4,045,977 describes a self-operating excess refrigerant storage system for a heat pump. This system includes an expansion valve, a filter-drier, and a unidirectional check valve which bypasses the expansion valve.
No device is known that can combine the functions of a pair of filter-driers within a single apparatus so that heat pump systems can be simplified and the costs thereof can be lowered. There is accordingly a need for a filter-drier which can perform its function when the liquid is flowing in either direction within the high-pressure liquid lines of a heat pump system.